Benthic Total Maximum Daily Load Study y yfor Accotink Creek

Public MeetingJuly 26, 2010

Presentation Outline

• TMDL Background

• Accotink Creek Impairment History

• Stressor Analysis

Why are we here?

Accotink Creek does not meetAccotink Creek does not meet Virginia’s Water Quality 

Standards.

‐ How do we know standards  ’ b i ?aren’t being met?

‐ Why doesn’t Accotink Creek meet standards?

‐ What is being done to correct the problem?

How do we know that Accotink Creek doesn’t t W t Q lit St d d ?meet Water Quality Standards?

• Perform physical, biological, and chemical monitoring on water bodies throughout the state

• Monitor parameters such as:

⁻ pH⁻ TemperatureDissolved Oxygen⁻ Dissolved Oxygen

⁻ Biological Community⁻ Bacteria⁻ Nutrients⁻ Fish Tissues⁻ Metals/Toxic Pollutants/

What do we do with the monitoring data h i ll d?

Compare the data collected to the

that is collected?

Compare the data collected to the water quality standards

Water Quality Standards:Water Quality Standards:• Regulations based on  federal and state lawS t i d ti• Set numeric and narrative limits on pollutants

• Consist of designated use(s) and water quality  criteria to protect the  designated usesdesignated uses

Designated Uses

• Recreational 

• Public Water Supply

• Wildlife

• Fish Consumption

• Shellfish

• Aquatic Life

Th tt i t f th ti lif i l t d b t ti f th h lthThe attainment of the aquatic life use is evaluated by testing for the health of the benthic macroinvertebrate community, as well as for parameters such as DO and pH.

Accotink Creek Benthic Impairments

YImpaired 

UseImpairment Cause

Impairment Length

Year Impairment First Listed

Upstream LimitDownstream 

Limit

Aquatic Benthic Confluence withStart of the tidal 

Aquatic Life 

Benthic Macroinvertebrates

7.35 miles 1996Confluence with Calamo Branch

waters of Accotink Bay

Aquatic Benthic

Confluence of an unnamed tributary, 

Confluence withAquatic Life 

Benthic Macroinvertebrates

0.85 miles 2008 located in the upstream corridor of 

Ranger Park

Confluence with Daniels Run

What happens when a water body doesn’t t t lit t d d ?meet water quality standards?

• Waterbody is listed as “impaired” and placed on the 303(d) list.

• Once a water body is listed as impaired, a Total i il d l b d l d f hMaximum Daily Load value must be developed for that 

impaired stream segment to address the designated use impairment. p

• TMDL Studies are required by law:

• 1972 Clean Water Act (CWA)• 1972 Clean Water Act (CWA) 

• 1997 Water Quality Monitoring Information and Restoration Act (WQMIRA)Restoration Act (WQMIRA)

Wh t i TMDL ?What is a TMDL ?Total Maximum Daily Loady

TMDL = Sum of WLA + Sum of LA + MOSTMDL   Sum of WLA   Sum of LA   MOS

Where:Where:

TMDL    =    Total Maximum Daily LoadWLA W t L d All ti ( i t )WLA       =    Waste Load Allocation (point sources)LA  =     Load Allocation (nonpoint sources)MOS       =    Margin of Safety

TMDL Development Methodology

1. Benthic TMDL:  Determine most likely stressor, then identify sources of that 

35%

stressor.2.  Calculate the amount of pollutant 

entering the stream from each source 

15%

20%

25%

30%

35% type.

3.  Enter available data into a computer model.  Model simulates pollutant 

0%

5%

10%

Source A Source B Source C Source D Source E

loadings into the watershed.

4.  Use the model to calculate the pollutant reductions needed by source to attain

5.   Allocate the allowable loading to each source and include a

reductions needed, by source, to attain Water Quality Standards.

each source and include a margin of safety.

Project HistoryProject History• TMDL Study initially began in 2007

• December 2007 – Revised timeline for project completion

• EPA assumes the lead in TMDL Development – May 2009

T h i l Ad i C itt M ti• Technical Advisory Committee Meetings

‐ December 2008, August 2009, January 2010

• Public Meetings• Public Meetings

– September 2009

– July 2010y

• Public Comment Period on Draft Report:  

July 5, 2010 to August 4, 2010

Average VSCI Score 1994 - 2008

Biological Monitoring Data

• VSCI scores in the Accotink Creek have been consistently low.  Overall average of 33.9 (1994 – 2008)

5060708090

100

I Sco

re

Average VSCI Score 1994 - 2008VSCI 60 Cutoff

• Habitat Scores remain in the 6‐7 range and organism density continues to be low. 0

1020304050

1AACO014.57 1AACO009.14 1AACO006.10 1AACO006.10 1AACO002.50

Aver

age

VSC

I

• Dominant organisms at these stations are from the families Hydropsychidae and Chironomidae (considered to be more

(2007) (2008) (1994-1996) (2006-2008) (2006-2007)

Station

MFBI Scores in Accotink Creek

VSCI = Virginia Stream Condition Index

Chironomidae (considered to be more tolerant).

6.07.08.09.0

10.0

core

MFBI Scores in Accotink Creek

0.01.02.03.04.05.0

1AACO014.57 1AACO009.14 1AACO006.10 1AACO006.10 1AACO002.50

MFB

I Sc

(2007) (2008) (1994-1996) (2006-2008) (2006-2007)

Monitoring Station

MFBI = Modified Family Biotic Index, adapted from Hilsenhoff’s Biotic Index (HBI),

Data Used in Stressor Identification1. Biological and Habitat Assessment Data 

‐ Collected between 1996 and 2008 at four VA DEQ monitoring stations

2. Water Quality Data‐ Instream water quality data (field parameters, nutrients, solids, metals,   and organic contaminants)g )

‐ Collected between  1974 and 2008 at eight VA DEQ monitoring stations

3. Toxicity Testing (EPA Region 3 laboratory in Wheeling, West Virginia): ‐ Using  water samples from two VA DEQ monitoring stations

a) Acute toxicity testing b) Chronic toxicity testing

4. Discharge Monitoring Reports (DMR)

5 Relative Bed Stability Studies (RBS)5. Relative Bed Stability Studies (RBS)

6. Biologist’s field notes and observations (VA DEQ)

Stressor Identification

Non‐Stressors*

pHpH

Temperature

Dissolved Oxygen

Instream Metals

Possible Stressors**

Nutrients (Nitrogen and Phosphorus)( g p )

Toxicity

Metals and Organic Contaminants in Fish Tissue

Most Probable Stressors***

* Non‐Stressors ‐ Stressor without water quality exceedances

Most Probable Stressors***

Urban Runoff and Sedimentation (Instream Erosion)

 Non‐Stressors ‐ Stressor without water quality exceedances** Possible Stressors ‐ Stressor with data indicating possible links to benthic impairment.*** Most Probable Stressors ‐ Stressor with conclusive data linking it to the poor health of the  

benthic community.

Relative Bed Stability Analysis

LRBS Percentile in Accotink Creek

Station ID LRBS Percentile1

Mean Particle Size Percentile in Accotink Creek

Station IDLog of Mean Particle Size

Percentile1

1AAC004.84 ‐0.04 88th

1AAC006.10 (2006) 0.55 98th

1AAC006 10 (2008) 0 56 95th

Particle Size

1AAC004.84 1.17 73rd

1AAC006.10 (2006)

1.57 98th

1AAC006 10 1AAC006.10 (2008) 0.56 95th

1AAC009.14  0.72 99th

1Based on Statewide Data

1AAC006.10 (2008)

1.35 79th

1AAC009.14  1.44 83rd

1Based on Statewide Data

Percent Fines Percentile in Accotink Creek

Station ID Percent Fines Percentile1

Slope Percentile in Accotink Creek

Station ID Slope Percentile1

1AAC004.84 18% 15th

1AAC006.10 (2006) 19% 18th

1AAC006.10 (2008) 24% 20th

1AAC004.84 0.52 30th

1AAC006.10 (2006) 0.22 14th

1AAC006.10 (2008) 0.17 11th

1AAC009.14 19% 18th

1Based on Statewide Data

1AAC009.14 0.22 14th

1Based on Statewide Data

Most Probable Stressordi i d b ff ( i )Sedimentation and Urban Runoff (Instream Erosion): 

‐ Low habitat assessment scores for epifaunal substrate, sedimentation, embededness, bank stability, etc.

‐ RBS Study Results:  ‐ Altered hydrology has led to a scoured, eroded stream which leaves behind a higher 

than expected median particle size. ‐ Fine sediments transported out of the upper reaches of Accotink Creek.  Sediment p pp

that erodes from the banks of Accotink Creek is deposited further downstream in the Accotink watershed, closer to the tidal boundary. 

‐ DEQ Field Biologists noted impacts from nonpoint source and storm sewer runoff were d di h bi d i ll i hibi i h h l h f h i idegrading habitat and potentially inhibiting the health of the aquatic community.

‐ The impervious surfaces within the urban areas have increased the overland flow, high flow events, and channel erosion.

‐ Flow frequency analysis (City of Fairfax, July 2005) showed that the frequency of high stream flow events increased and the baseflow decreased with increased imperviousness.

High urban runoff leading to excessive instream erosion are considered to be the most probable stressors impacting the biological community in Accotink Creek. 

CDEQ Contact Information

CO

Bryant ThomasVirginia Department of Environmental QualityWater Quality Programs Manager – Northern Regional Office

NT

Water Quality Programs Manager – Northern Regional OfficePhone: (703) 583‐3843E‐mail:  Bryant.Thomas@deq.virginia.gov

TA

Katie ConawayVirginia Department of Environmental QualityRegional TMDL Coordinator – Northern Regional OfficeA

CPhone: (703) 583‐3804E‐mail:  Katie.Conaway@deq.virginia.gov

TS

Craig LottVirginia Department of Environmental QualityTMDL Modeling Coordinator – Central OfficePh (804) 698 4240S Phone: (804) 698‐4240E‐mail:  Craig.Lott@deq.virginia.gov

Pollutant of Concern = SedimentPollutant of Concern Sediment

Sediment ↔ Flow RelationshipSediment ↔ Flow RelationshipAccotink Creek Sediment Rating Curve

y = 13.56x1.3847

R2 = 0.7557100000

1000000

1000

10000

TSS (lb

/day)

100

T

1

10

1 10 100 1000

Flow (cfs)

Accotink Creek TMDL ApproachAccotink Creek TMDL Approach

• Reductions for a surrogate (stormwater runoff)Reductions for a surrogate (stormwater runoff) are established to achieve reductions for the pollutant (sediment)

• Stormwater is an appropriate surrogate because the pollutant (sediment) load in Accotink Creek is a function of the amount of stormwater runoff generated in the Accotink Creek watershed Thi TMDL bli h li i f h f• This TMDL establishes a limit for the amount of stormwater runoff that Accotink Creek can receive during storm eventsreceive during storm events.

Regulatory Authority• CWA 304(a)(2): “The Administrator …shall develop and

publish information on the factors necessary to restore and

Regulatory Authority

publish…information on the factors necessary to restore and maintain the chemical, physical, and biological integrity of all navigable waters . .

• CWA 304(f)(2)(F): “The Administrator…shall issue. . .information including . . . processes, procedures, and methods to control pollution resulting from . . . changes in the movement, flow, or circulation of any navigable waters or ground waters...”y g g

• CWA 402(p): sets forth the authority to regulate discharges composed entirely of stormwater from industrial and municipal stormwater systems Section 402(p) treats dischargers ofstormwater systems. Section 402(p) treats dischargers of stormwater associated with industrial and construction activity and certain municipal dischargers as point sources and subject to NPDES permits.

Regulatory AuthorityRegulatory Authority• CWA § 502(6) definition of pollutants:

“dredged spoil solid waste incinerator residue sewage garbagedredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste di h d i t t ”discharged into water”

• CWA § 502(19) definition of pollution:“man-made or man-induced alteration of the chemical, physical, p ybiological, and radiological integrity of water”

• Flow is a type of pollution• Federal Regulations at 40 CFR 130 7:Federal Regulations at 40 CFR 130.7:

– Identify list of pollutants to be regulated, and– Develop TMDLs for pollutants identifiedp p

Regulatory Authority• EPA implementing guidance for identification of impaired

waters:

Regulatory Authoritywaters:– If impairment is caused by pollution and not

pollutants, no TMDL is needed – If impairment is caused by pollution that is

associated with pollutants, a TMDL is needed• If excess stormwater flow causes impairment due toIf excess stormwater flow causes impairment due to

associated pollutants (like sediment, toxics, etc), a TMDL is required

• EPA believes a TMDL can be expressed in terms of• EPA believes a TMDL can be expressed in terms of stormwater flow volume or flow reduction, where “flow” is used as a surrogate for pollutants associated with stormwater dischargesstormwater discharges

Regulatory Authority

• Code of Virginia § 62 1-11(F):

Regulatory Authority

Code of Virginia § 62.1 11(F):“The quality of state waters is affected by the quantity of water andaffected by the quantity of water and it is the intent of the Commonwealth, t th t t ti bl t i t ito the extent practicable, to maintain flow conditions to protect instream b fi i l d bli tbeneficial uses and public water supplies for human consumption”

Agenda

• Overview of the Technical Approach

• Attainment Streams

• Selection of Hydrologic TargetSelection of Hydrologic Target

• TMDL Allocations

Questions• Questions

TMDL Development

Based on the Attainment Watershed Approach

1. Selection of Appropriate Attainment Streams where the VADEQ Aquatic Life Criteria are currently met

2. Development of Flow Durations Curves (FDC) for Accotink Creek and the Attainment Streams

3. Identification of the Hydrologic Endpoints

4 Estimation of the Existing Conditions Stormwater Flow4. Estimation of the Existing-Conditions Stormwater Flow In Accotink Creek and the TMDL Stormwater Flow

5 Development of the TMDL Allocations5. Development of the TMDL Allocations

Criteria Used in the Selection of Attainment Streams

• Existing biological monitoring data indicating that the stream is not impaired

• Existing USGS Gage Station located in close proximity to a DEQ Biological Stationg

• Biological Station is located in either the Piedmont or Northern Piedmont eco-region (Most of the drainage area of g ( gthe Accotink Creek watershed is within these 2 Ecoregions)

• Drainage Area at the USGS Station has to be greater thanDrainage Area at the USGS Station has to be greater than 10 mi2 and less than 100 mi2 (Accotink drainage area is 24 mi2 at the gauging station and about roughly 51 mi2 at the outlet of the impairment). This generally corresponds to the same stream order as Accotink Creek.

Selection of Attainment Streams

Attainment Streams

Stream E i USGS Period of Fl

Drainage AStream

Name Ecoregion USGS Station Flow

RecordArea(mi2)

Buffalo Creek Piedmont 02039000 1946-2009 69.6

Catoctin N th Pi d t 01638480 1971 2009 89 5Creek Northern Piedmont 01638480 1971-2009 89.5

Northern PiedmontAccotinkCreek

Northern Piedmont, Piedmont,

Southeastern Plain01654000 1947-2009 23.9

Attainment Streams Biomonitoring DataVirginia SCI Scores

Collection Buffalo Catoctin Collection Buffalo Catoctin Period Creek Creek

Fall 1994 - 70.5Spring 1995 - 73.1Fall 1995 66 2

Period Creek CreekFall 2000 - 68.5Spring 2001 - 69.6Fall 2001 67 1Fall 1995 - 66.2

Spring 1996 - 67.0Fall 1996 - 63.1Spring 1997 - 72 8

Fall 2001 67.1Spring 2002 63.5 75.48Fall 2002 69.0 68.74Spring 2003 - 54 99Spring 1997 - 72.8

Fall 1997 - 75.5Spring 1998 - 74.7Fall 1998 - 69.7

Spring 2003 - 54.99Fall 2003 - 66.7Fall 2005 77.8 -Spring 2006 61.0 -a 998 69

Spring 1999 - 74.0Fall 1999 - 71.1Spring 2000 - 71.7

Sp g 006 6 0Fall 2006 80.8 -Spring 2008 70.6 61.4Fall 2008 68.8 -

Flow Duration Curves

• The hydrologic target is identified using cumulative frequency curves, called Flow Duration Curves (FDCs)

• FDCs depict the percentage of time that specific daily flows are equaled or exceeded at sites where continuous records of daily flow are available

• FDCs have been widely used for quantifying andFDCs have been widely used for quantifying and studying the effects of urbanization on streams, since they respond to changes in a watershed’s hydrologic characteristicscharacteristics

• FDCs are constructed using observed flow data that is dil il blreadily available

Flow Duration Curves

• Flow duration curves are developed for Accotink Creek (impaired stream) and a composite FDC representing the attainment streams (Buffalo Creek and Catoctin Creek)attainment streams (Buffalo Creek, and Catoctin Creek)

• In order to compare the FDCs and identify the endpoint, the FDC are de eloped sing to flo per nit area (c bicFDC are developed using to flow per unit area (cubic feet/acre-day)

Th it Att i t t FDC bi d• The composite Attainment streams FDC combines and uses the average unit-area flows for Buffalo Creek and Catoctin Creek

• FDCs are developed using a similar period of record; a 20-year period of flow record (November 1989 through November 2009) is used to develop the FDCs2009) is used to develop the FDCs

Flow Duration Curves

Selection of Hydrologic Targets

• The Accotink Creek TMDL establishes targets for high and low flows

– The high-flow target is the 1year-24 hour stormwater flowg g y

– The low-flow target is the 95th percentile flow (flows are l d d d 9 % f h i )equaled or exceeded 95% of the time)

Reductions to the high flow target will result inReductions to the high flow target will result in increased infiltration and groundwater recharge and will ultimately result in achieving the low-flow target

Selection of Hydrologic Targets

The 1 year-24 hour flow was selected as the high flow target:

1 Stream channel morphology is more influenced by frequent1. Stream channel morphology is more influenced by frequent (1- to 2-year) flow events; “bankfull” or “near bankfull” flows; than by large flood events (Leopold 1994, Hollis 1975)

2. The 1 year-24 hour flow is generally considered the channel forming flow for small streams

3. Targeting the channel forming flow helps directly reduce key channel altering events that produce large amounts of sediment within the stream system and damage the aquaticsediment within the stream system and damage the aquatic habitat

4 Virginia has proposed design specifications for stormwater4. Virginia has proposed design specifications for stormwater management measures that are largely based on controlling the 1 year-24 hour flow

1 year-24 Hour Hydrologic Target

Th 1 24 h t t fl i ti t d t 234 f

1 year-24 Hour Hydrologic Target • The 1 year-24 hour stormwater flow is estimated at 234 cfs

using the last 20 year of flow record in Accotink Creek (November 1989 through November 2009) and corresponds to:

– A unit-area flow of 1,321.7 ft3/acre-day using the Accotink Creek FDC, and– A unit area flow of 639,8 ft3/acre-day using the attainment-streams

composite FDC p

Estimation of Overall TMDL Stormwater Flow Reduction for a one-year, 24- hour flow

A ti k C kAccotink Creek

Flow Volume (ft3)

Accotink Creek Unit-Area Flow

Volume(ft3/acre-day)

Non-impaired Composite Unit-Area Flow Volume

(ft3/acre-day)

Flow Volume Reduction

(ft3/acre-day)

Overall Reduction

20,217,600 1,321.7 681.8 639.9 48.4%

Overall, the magnitude of the one-year 24-hour stormwater flow in the Accotink Creek watershed must be reduced by 48.4% in order to meet the

established TMDL endpoints

Existing Conditions Flow Distribution

• Distribution of the 1year-24 hour flow existing-conditions in Accotink Creek was based on:

– A land-use based approach to estimate the relative stormwater flow contribution from the land areas

– A Runoff Coefficient Approach to estimate the existing stormwater contribution from each land use gcategory

– A runoff coefficient (Rc) represents the fraction ofA runoff coefficient (Rc) represents the fraction of precipitation that appears as runoff and is expressed as a constant value between zero and one

Runoff Coefficient (Rc) = 0.05 + 0.91*Fraction of Imperviousness

Accotink Creek Existing Conditions Unit Area Flow 1 Year-24 Hour Flow

Accotink Creek Existing Conditions Unit-Area Flow Volume (one-year, 24-hour flow)

Fairfax County Land Use Type Acres Percent Imperviousness*

Runoff Coefficient

Flow (ft3/acre-

day)High Density Residential 3 003 31 0 332 155 7High Density Residential 3,003 31 0.332 155.7Medium Density Residential 7,655 25 0.278 331.6Institutional 1,464 24 0.268 61.3Industrial 1,949 38 0.396 120.4High Intensity Commercial 757 52 0.523 61.8Low Intensity Commercial 843 42 0.432 56.9Transportation 4,566 27 0.296 210.8Estate Residential 383 21 0.241 14.4383 0. .Golf Course 686 9 0.132 14.1Low Density Residential 3,286 22 0.250 128.3Open Space 5,715 15 0.187 166.4

T t l 30 307 1 321 7Total 30,307 - - 1,321.7* Percent Imperviousness Derived using GIS data provided by Fairfax County

Basis for Developing the Allocations

• 10% of the existing stormwater flow from all land uses was used to calculate the LA assigned to nonpoint sources

• WLAs are based on the assumption that stormwater runoff from 90% of all land uses in the watershed drain to permitted storm sewer systems

• Equal reductions to the existing stormwater flow (LA and WLA) contribution from all the land use categories except for the Opencontribution from all the land use categories except for the Open Space land use category

TMDL Waste Load Allocations (WLA)

Land Use Category Acres

Existing conditions(ft3/acre-

Allocation(ft3/acre-

day)Reduction

day) day)

High Density Residential 2,702.7 140.1 62.51 55.4%Medium Density Residential 6,889.5 298.4 133.14 55.4%

Institutional 1,317.6 55.2 24.63 55.4%Waste Load Allocations

Industrial 1,754.1 108.4 48.35 55.4%High Intensity Commercial 681.3 55.6 24.82 55.4%Low Intensity Commercial 758.7 51.2 22.84 55.4%

Transportation 4,109.4 189.7 84.62 55.4%Estate Residential 344.7 13.0 5.79 55.4%

Golf Course 617.4 12.7 5.67 55.4%Low Density Residential 2957.4 115.5 51.53 55.4%

Open Space 5,143.5 149.7 149.74 0.0%Total 27,276 1,189.5 613.6 48.4%

This WLA is disaggregated to develop specific allocations for each MS4 and Stormwater Permit (Industrial, General, etc..)

TMDL Load Allocations (LA)

Land Use Category Acres

Existing conditions(ft3/acre-

Allocation(ft3/acre-

day)

Reduction

Load Allocations(Lands not

(day) day)

High Density Residential 300.3 15.6 6.95 55.4%Medium Density

R id ti l 765.5 33.2 14.8 55.4%(Lands not discharging to an MS4 - 10% of the

existing stormwater fl

ResidentialInstitutional 146.4 6.1 2.7 55.4%

Industrial 194.9 12.0 5.4 55.4%High Intensity Commercial 75.7 6.2 2.76 55.4%

i C i l 84 3 2 4 4%flow) Low Intensity Commercial 84.3 5.7 2.54 55.4%Transportation 456.6 21.1 9.40 55.4%

Estate Residential 38.3 1.4 0.64 55.4%Golf Course 68.6 1.4 0.63 55.4%

Low Density Residential 328.6 12.8 5.73 55.4%Open Space 571.5 16.637 16.64 0.0%

Total 3,031 132.2 68.2 48.4%

Disaggregation of the WLA

•Set aside 5% of the total TMDL for construction stormwater it Th f t t ti ti iti d tpermits. The future construction activities are assumed to occur

in all land use categories including the Open Space category

•Industrial stormwater permits: Individual, general stormwater, and concrete facilities

•MS4 Permits (VDOT, Fairfax County, City of Fairfax, Town of Vienna, Fort Belvoir Military Reservation)

Summary of Existing and Allocated Stormwater Flows

Summary of Existing and Allocated Stormwater Flows

Stormwater Flows

Source Allocation Category Acres

Existing Conditio

ns (ft3/acre-

Allocation

(ft3/acre-day)

Percent Reducti

onday) -day)

P i t S

MS4 Permits 25,237.7 1,086.1 551.9 49.2%

Construction Stormwater Permits 1 515 4 76 4 34 1 55 4%Point Sources (WLA)

Construction Stormwater Permits 1,515.4 76.4 34.1 55.4%

Industrial Stormwater Permits 674.8 34.6 15.44 55.4%

WLA Totals 27,427.8 1,197.2 601.42 49.8%

Nonpoint Sources (LA) 2,879.2 124.5 63.74 48.8%

Grand Total 30,307 1,321.7 665.16 49.7%

MS4 Permittees Wasteload Allocations

Reduction to the one yearMS4 Acres Reduction to the one-year, 24-hour Flow

Fairfax County 20,071.3 48.4%Ci f F i fCity of Fairfax 2,848.0 53.2%Town of Vienna 945.3 53.2%Fort Belvoir 873.6 41.8%Fort Belvoir 873.6 41.8%VDOT 433 55.4%NOVA Community College 66.7 54.9%

T t l 25 237 7 49 2%Total 25,237.7 49.2%

Drainage WLA Reduction of 1 year

Individual and Industrial Stormwater Permits

Facility Name Permit Number Area (acres) 24 hour Flow

Individual VPDES Stormwater PermitsFairfax Terminal Complex VA0001872 106.4 55.4%Kinder Morgan Southeast Terminals VA0001945 17.9 55.4%Motiva Enterprises LLC VA0001988 10.9 55.4%Motiva Enterprises LLC - Fairfax VA0002283 4.6 55.4%Quarles Petroleum - Newington VA0057380 3.6 55.4%

Industrial Stormwater General PermitsCanada Dry - Springfield VAR050988 4 55.4%SICPA Securink Corporation VAR051042 7.5 55.4%Connector Bus Yard VAR051047 6.3 55.4%United Parcel Service VAR051053 2 55.4%US Postal Service - Merrifield VAR051066 1.8 55.4%Fort Belvoir Building 1442 VAR051080 430.7 55.4%Shenandoahs Pride Dairy VAR051100 7.3 55.4%Federal Express Corporation VAR051109 3.9 55.4%G and L Metals VAR051134 1 55.4%Rolling Frito Lay Sales LP VAR051565 4.1 55.4%

National Asphalt Paving Corporation VAR051719 2 7 55.4%National Asphalt Paving Corporation VAR051719 2.7

Jermantown Maintenance Facility VAR051770 10.8 55.4%Newington Maintenance Facility VAR051771 25 55.4%DVS - Alban Maintenance Facility VAR051772 4.7 55.4%HD Supply - White Cap VAR051795 0.2 55.4%pp y pUnited Parcel Service - Newington VAR051863 13.7 55.4%

Concrete Facilities Stormwater General PermitsNewington Concrete Corporation VAG110046 1.2 55.4%Virginia Concrete Company VAG110069 4.5 55.4%

Total 674.8 55.4%

TMDL Equations

Stormwater TMDL for Accotink Creek (ft3/acre-day)

TMDL Load Allocation Wasteload Allocation Margin of Safety

665.2 63.7 601. 4 Implicit/Explicit

Stormwater TMDL for Accotink Creek (Reduction to the one-year- 24-hour flow)

L dTMDL Load Allocation Wasteload Allocation Margin of Safety

49.7% 48.8% 49.8% Implicit/Explicitp p

Questions & Comments

Comment period ends August 4, 2010Submit comments to:Submit comments to:

Gregor VoigtGregory VoigtOffice of Standards, Assessment and TMDLs (3WP30)

US EPA Region III1650 A h St t1650 Arch Street

Philadelphia, PA 19103215-814-5737

i @voigt.gregory@epa.gov